MOLECULAR BIOLOGY AND GENOMICS OF FOODBORNE PATHOGENS
Location: Produce Safety and Microbiology Research
Title: Stability of Green Tea Catechins in Commercial Tea Leaves during Storage for 6 Months
Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 25, 2008
Publication Date: March 20, 2009
Citation: Friedman, M., Levin, C.E., Lee, S., Kozukue, N. 2009. Stability of Green Tea Catechins in Commercial Tea Leaves during Storage for 6 Months. Journal of Food Science. 74(2):47-51.
Interpretive Summary: As part of an effort to relate composition of teas to antimicrobial activities against foodborne pathogens, including ongoing studies on inactivation of Salmonella bacteria on peanuts, we noted that tea bags stored for long periods of time lose some their biologically active catechins. To better define the significance of storage-induced changes, we did a statistical analysis of the results of changes in individual and total catechin levels as a function of storage time of teas sold in the United States, Korea, and Japan. The results indicate a progressive decrease in the content in individual and total levels of seven catechins during a six-month storage period. The described observations will hopefully stimulate additional needed studies on the stabilities of tea catechins in green and theaflavins in black tea leaves throughout the harvesting, processing, marketing, storage, and consumption of teas and tea products. The results, based on a collaborative study with a Korean University, suggest that consumers may benefit from knowing the storage history of teas sold at retail. A manuscript on this subject will be published in the March 2009 issue of the Journal of Food Science.
To help meet the needs of consumers, producers of dietary tea products, and researchers for information on health-promoting tea ingredients, we determined by HPLC seven catechins [(–)-epigallocatechin (EGC), (–)-catechin (C), (+)-epicatechin (EC), (–)-epigallocatechin 3-gallate (EGCG), (–)-gallocatechin 3-gallate (GCG), (–)-epicatechin 3-gallate (ECG), and (–)-catechin 3-gallate (CG)] in samples of eight commercial green tea leaves of unknown history sold as tea bags in the United States, Korea, and Japan. The samples were stored at 20 °C and sampled at 1 week, 1 months, 2 months, 4 months, and 6 months. The following ranges in the initial values controls were observed (in mg/g tea leaves): EGC and C, 0 to trace amounts; EC, 1.9-21.1; EGCG, 13.3-113.0; GCG, 0.2-1.6; ECG, 5.7-50.5, CG 0.5-3.7; total catechins 36.5-169.7. Statistical analysis of the results and plots of changes in individual and total catechin levels as a function of storage time indicate a progressive decrease in the content in the total levels, most of which is due to losses in the most abundant catechins, EGCG and ECG. Possible mechanisms of degradations of catechins during storage and the possible significance of the results to consumers of tea are discussed.